RB25 - replacing conrod bearings

[hardsteppa]

hey team

picked up a spare RB25 short block and looking at a project rebuild, but in the meantime I have concerns about minor conrod bearing damage in the rb25 currently in the car. As a set of bearings is cheap-as, and from research done so far, provided there's no damage to the crank, no machining is needed to replace with new bearings (only 2 sizes according to workshop manual, with most sizes being standard 0?). So to get what I can out of the current motor I'm thinking, drop the sump and replace the conrod bearings with the engine still in the car. Any words of warning or potential issues in doing this? Obviously won't be able to check clearances but as above from what I can gather as long as using the same size stock bearing, with no damage or machining being done this shouldn't be an issue?

 

[boostn0199]

Still a good idea if you have it all open to get a mic and bore gauge and measure everything up and compare if all is within spec and whether your happy with the clearances you will get with just using the oem bearing grades.

[tridentt150v]

On 05/07/2016 at 6:24 PM, hardsteppa said:

hey team

I have concerns about minor conrod bearing damage in the rb25 currently in the car.

 

Why do you think this?  Have you taken the sump off and popped a bearing for a look then put it back?  Usually in a motor if the big ends are shot then the motor is tired and needs a refresh anyway.  And unless your doing a quick and dirty to sell [and moral issues here] or flog to the limiter, I wouldn't do it. 

[hardsteppa]

thanks for the inputs, appreciated.

The thing is, as mentioned, the bearings are cheap-as - I got a set of Nissan/NDC bearings for $49 delivered. I wouldn't even drain the oil, pull off the sump and pull apart the rods, clean the sump and put it all back together only to have to do it all again, for $49; I'd rather just spend that and have them ready to go in the first time rather than doing it twice and costing more in my time and parts...and if I already have them, and they will fit just fine in a stock/unmachined crank as I queried above, then I might as well just put them in the first time while I have it apart. So that really leads back to the original post; not 'is it worth putting in new ones', because if I'm pulling it apart to check current condition then it's definitely worth it...just more, are there are any issues in putting stock bearing sizes in, matched to numbers stamped on the crank, without any refinishing/crank polishing etc.

[hardsteppa]

or to put 'any issues' into risk management terms ; what's the likelihood of a risk occurring and the severity of the risk should it occur.

[AngryRB]

What about using some plastiguage to check clearance's of the old and the new etc.. once at that stage though the nissan has escaped and bit of a worry..

[hardsteppa]

just for the reference I did put the new bearings in a while back and while a bit of a mission, easier than pulling the engine out. All went in without issue, running sweet as 6 months down the track. So for $50 and a few man hours, worth it.

A tip for anyone though, when putting the sump back on, ditch a few of the bolts and put in a few M6 studs of varying length instead. Makes it ALOT easier to get the sump back on into the right place first time without smearing gasket sh&t everywhere.